Tech job growth has transformed some cities into office powerhouses, such as San Francisco, which has the effect, in some cases of tenants seeking lower rents and less expensive labor in cities such as Phoenix and Austin, Texas.

Jobs have shot up at a healthy clip in the top tech markets. For example, San Francisco saw a 47 percent jump in its high-tech job base from 2013 to 2015, to almost 70,000 workers, according to a recent report by CBRE. In Phoenix, high-tech job growth was 45 percent from 2013 to 2015, to almost 50,000 workers. Both Austin and Charlotte, N.C., had jumps in high-tech jobs of about 33 percent in that timeframe, according to the CBRE report.

The tech sector has grown to account for one-fifth of all office leasing today, says Colin Yasukochi, director of research and analysis at CBRE. The 30 top tech markets all saw office job growth of more than 16 percent, outpacing the national average of 13.7 percent. However, demand for tech talent in top markets, such as San Francisco, Silicon Valley and New York City, far outpaces supply, forcing universities and governments to scramble to attract students into hot job fields.

“The schools and cities see a competitive advantage of channeling resources to attracting tech students, and the companies are working with the federal government to expand the visa programs to get more people into the country with the proper skills,” Yasukochi says.

The markets at the high-end of the job growth spectrum are seeing sharply increasing rents and decreasing vacancies, he says. San Francisco has held the throne of high-tech jobs king for five years, with technology companies dominating office leasing in the city. Tech space accounts for 54 percent of all leasing in San Francisco, and has boosted net office space absorption by almost 11 percent the past two years, CBRE says. Rents increased to $65.20 per sq. ft. in the third quarter, and vacancies leveled off at around 9 percent due to a lull in the tech markets in the first half. But some analysts suggest that the IPO market could come roaring back after the election, fueling a new round of growth, according to a third-quarter Savills Studley report.

Yasukochi says the frenetic pace set by San Francisco leasing has landlords firmly in charge, enough so that tenants are looking to other markets for talent and cheaper rents. He points to Phoenix and surrounding cities as a more stable, spread-out market that has room to grow. The city’s vacancy rate is twice that of San Francisco’s, while the rents are one-third the cost, according to the Savills Studley report. Downtown Tempe and Scottsdale are leading the office growth in the Phoenix market and the city’s warehouse district is getting an overhaul to attract tech tenants, Yasukochi says.

“You have to think that it’s not just the office space to consider, it’s also the cost of living for your employees, the housing costs—some top talent will go elsewhere,” he says. “In Phoenix, it’s more suburban, the clusters tend to be more dispersed.”

The bubble can’t last forever, Yasukochi says, and just like most industries, tech office will tumble in when the cycle turns. However, he says he doesn’t see another dot-com bust. “I think it’s a long-term growth story, and has established itself as a top industry,” he says. “I think we’re a lot more stable than we were at the turn of the century.”